定时器中改变PWM值的问题

/* EPwm1Regs.CMPA.half.CMPA = 1500+(SINA[motor1.motorStepCount]/2)*0.3;
EPwm2Regs.CMPA.half.CMPA = 1500+(SINA[motor1.motorStepCount]/2)*0.3;
(*ePWM[2]).CMPA.half.CMPA = 1500+(SINA[(motor1.motorStepCount+60)%240]/2)*0.3;
(*ePWM[3]).CMPA.half.CMPA = 1500+(SINA[(motor1.motorStepCount+60)%240]/2)*0.3;*/

我在定时器中加入这段代码时，发现这段代码运行花了100us的时间，这是咋回事。时PWM值更新设置问题？